Imaging spectrometers operable to form high-resolution images in a wide range of spectral bands are used in scientific, military, and resource-sensing applications. In one form of the imaging spectrometer, an objective optic forms an image of a scene at a slit. One portion of the scene is imaged by a panchromatic detector located at the image plane. A double-pass collimating-and-imaging optic receives another portion of the image passed through the slit and directs it to a dispersive element. The dispersed image is passed back through the collimating-and-imaging optic to a two-dimensional hyper-spectral imaging detector array located at the plane of the slit. One dimension of the array contains spatial information, and the other dimension contains spectral information. To view and spectrally analyze a two-dimensional scene, the entire imaging spectrometer is scanned in a direction perpendicular to the slit. Existing imaging spectrometers use refractive optics, reflective optics, or a combination of the two.
While operable, the available imaging spectrometers have some shortcomings. They tend to suffer from a problem called “spectral smile”, which is an in-plane curvature of the spectral information provided by the hyper-spectral imaging detector. Additionally, they tend to have a relatively narrow field of view. The narrow field of view limits the lateral viewing range, and the spectral smile limits the usefulness of the results for some applications. For those cases where the optics contains refractive elements, there is a sensitivity to temperature changes and to the effects of radiation, particularly in a space environment.
There a need for an improved approach to an imaging spectrometer. The present invention fulfills this need, and further provides related advantages.